U.S. patent application number 13/203805 was filed with the patent office on 2012-01-12 for solid electrolyte gas sensor for measuring various gas species.
This patent application is currently assigned to ROBERT BOSCH GMBH. Invention is credited to Berndt Cramer, Dirk Liemersdorf.
Application Number | 20120006692 13/203805 |
Document ID | / |
Family ID | 42124499 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120006692 |
Kind Code |
A1 |
Liemersdorf; Dirk ; et
al. |
January 12, 2012 |
SOLID ELECTROLYTE GAS SENSOR FOR MEASURING VARIOUS GAS SPECIES
Abstract
In a sensor element for a solid electrolyte gas sensor,
comprising a gas-tight pumping chamber, a heater, a first pumping
electrode arranged in the pumping chamber, and an at least second
pumping electrode, an autonomous pumping cell is arranged as a gas
inflow restrictor instead of a diffusion barrier. The autonomous
pumping cell comprises an outer and an inner autonomous pumping
electrode which are contacted or short-circuited from outside by
means of a trimmable resistor.
Inventors: |
Liemersdorf; Dirk;
(Sachsenheim, DE) ; Cramer; Berndt; (Leonberg,
DE) |
Assignee: |
ROBERT BOSCH GMBH
Stuttgart
DE
|
Family ID: |
42124499 |
Appl. No.: |
13/203805 |
Filed: |
February 11, 2010 |
PCT Filed: |
February 11, 2010 |
PCT NO: |
PCT/EP2010/051713 |
371 Date: |
August 29, 2011 |
Current U.S.
Class: |
205/784 ;
204/424 |
Current CPC
Class: |
G01N 27/419
20130101 |
Class at
Publication: |
205/784 ;
204/424 |
International
Class: |
G01N 27/409 20060101
G01N027/409; G01N 27/407 20060101 G01N027/407 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2009 |
DE |
10 2009 001 249.4 |
Claims
1. A sensor element for a solid electrolyte gas sensor, which
comprises a pumping chamber, a heater and a first pumping electrode
arranged in the pumping chamber, as well as an at least second
pumping electrode, characterized in that an autonomous pumping cell
is arranged as a gas inflow restriction.
2. The sensor element as claimed in claim 1, characterized in that
the autonomous pumping cell comprises an outer autonomous pumping
electrode and an inner autonomous pumping electrode, which are not
contacted from the outside.
3. The sensor element as claimed in claim 2, characterized in that
the at least two pumping electrodes of the autonomous pumping cell
are operated while being ohmically loaded or electrically
short-circuited.
4. The sensor element as claimed in claim 3, characterized in that
the pumping properties of the autonomous pumping cell are
established by means of the ohmic load respectively set.
5. The sensor element as claimed in claim 2, characterized in that
the inner autonomous pumping electrode is arranged either in an
exhaust gas or in an air reference channel of the sensor
element.
6. The sensor element as claimed in claim 2, characterized in that
adaptation of the sensor element to the detection of different gas
species is carried out by modification of the outer autonomous
pumping electrode.
7. The sensor element as claimed in claim 1, characterized in that
the autonomous pumping cell comprises an outer autonomous pumping
electrode and an inner autonomous pumping electrode, which are
contacted from the outside by a controller by means of which the at
least two autonomous pumping electrodes can be modified from the
outside.
8. The sensor element as claimed in claim 7, characterized in that
a diffusion behavior or a gas inflow restriction, similarly as in
the case of a diffusion barrier, is simulated by means of the at
least two autonomous pumping electrodes which can be modified from
the outside.
9. The sensor element as claimed in claim 8, characterized in that
the electrical resistance of the at least two autonomous pumping
electrodes can be varied by means of the controller.
10. The sensor element as claimed in claim 1, characterized in that
the pumping chamber is sealed gas-tightly from a gas flow to be
detected.
11. The sensor element as claimed in claim 1, characterized in that
a Nernst voltage, which causes transport of oxygen into the pumping
chamber or out of the pumping chamber, is formed according to the
oxygen concentration gradient between a gas flow to be detected and
the autonomous pumping cell.
12. The sensor element as claimed in claim 2, characterized in that
the outer autonomous pumping electrode used is a mixed potential
electrode so that, depending on the electrode material, the sensor
element is suitable for the detection of further gas species.
13. The sensor element as claimed in claim 8, characterized in that
Pt, Pd, Ir, Ta or combinations of these materials or with further
constituents are used as electrode materials in the case of Nernst
electrodes, or Au, Ag, Cu, Zn or combinations of these and/or the
aforementioned materials are used in the case of mixed potential
electrodes.
14. The sensor element as claimed in claim 1, characterized in that
oxygen transport is balanced by ohmic loading of the autonomous
pumping cell by means of an electrical resistor.
15. A solid electrolyte gas sensor for the detection of gases,
characterized by a sensor element as claimed in claim 1.
16. A method for operating a sensor element as claimed in claim 1
for the quantitative detection of oxygen, the method comprising:
applying a constant voltage between the at least two pumping
electrodes (130, 405); and using the resulting electrical pumping
current as a measurement variable for the oxygen partial pressure
in an exhaust gas.
17. The method as claimed in claim 16, characterized in that
different states of the autonomous pumping cell (115, 410) are set
by means of the constant voltage applied to the pumping electrodes
(130, 405) and/or by the interconnection of the autonomous pumping
electrodes (415, 420) themselves.
18. The method as claimed in claim 16, characterized in that a
reduced pressure is set in the autonomous pumping cell (115, 410),
so that a positive pumping current is still generated in a rich
exhaust gas with a relatively low lambda value.
19. The sensor element of claim 13, wherein the further
constituents comprise ceramic components.
20. The sensor element of claim 19, wherein the ceramic components
comprise cermets.
21. The sensor element of claim 14, wherein the electrical resistor
comprises a trimmable resistor meander.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a sensor element for a solid
electrolyte gas sensor, to a corresponding solid electrolyte gas
sensor and to a method for operating such a sensor.
[0002] In the field of motor vehicle technology, wideband lambda
probes formed as solid electrolyte oxygen sensors are known, by
means of which the oxygen partial pressure or the residual oxygen
partial pressure of an exhaust gas can be measured. They consist of
a solid electrolyte in which a cavity used as a pumping chamber is
arranged, the latter being connected to the exhaust gas or a
corresponding combustion engine by means of a diffusion barrier.
These probes furthermore contain an air reference channel connected
to the ambient air.
[0003] In the case of oxygen-rich exhaust gas, oxygen is
electrochemically removed from said pumping chamber, the relevant
oxygen diffusion current being used as a measurement variable for
the oxygen partial pressure in the exhaust gas. In the case of an
exhaust gas with an oxygen deficit, the pumping direction is
reversed.
[0004] Besides said wideband probes, there are also proportional
probes which can be operated either in exhaust gas with an oxygen
excess or in exhaust gas with an oxygen deficit, but not for the
entire wideband range. As in the case of the wideband probe, oxygen
is also removed from a diffusion-restricted pumping chamber in
these probes. The oxygen diffusion current then continues as an
electrically measurable pumping current and is used as a
measurement variable for the oxygen partial pressure in the exhaust
gas. Since there is no information about the rich or lean state of
the exhaust gas owing to the lack of a control variable from the
unloaded Nernst cell, there is in this case no possibility of
pumping oxygen electrochemically into or out of the pumping chamber
as a function of the exhaust gas composition, so as to produce a
wideband probe.
[0005] So-called mixed potential sensors are furthermore known,
which are constructed in a similar way to a lambda step-change
probe and consist of an electrochemical cell, in which there is a
first platinum electrode in the exhaust gas. A second platinum
electrode is separated from the exhaust gas space by the solid
electrolyte and is in communication with the ambient air by means
of a said air reference channel.
SUMMARY OF THE INVENTION
[0006] The present invention is based on the concept, in a solid
electrolyte gas sensor of the type in question here, of arranging
an autonomous pumping cell as a gas inflow restriction in the
respective sensor element instead of said diffusion barrier.
[0007] In a preferred embodiment, the autonomous pumping cell
comprises two loaded or short-circuited pumping electrodes,
specifically an outer and an inner autonomous pumping electrode,
which do not need to be contacted from the outside. By the short
circuit or the ohmic load (i.e. using an ohmic load resistor) of
the outer and inner autonomous pumping electrodes, a migration
current is formed which is driven by the Nernst voltage or mixed
potential voltage that is formed. The pumping properties can be
established by means of the ohmic load respectively set.
[0008] In an alternative configuration, the autonomous pumping cell
is formed by an outer and an inner autonomous pumping electrode,
which are contacted or connected from the outside by/to a
controller, for example a control circuit, evaluation circuit or
the like, so that the at least two pumping electrodes can be
modified in-situ from the outside. By means of this controller, a
diffusion behavior is preferably simulated similarly as in the case
of a diffusion barrier, and preferably by varying the electrical
resistance of the two pumping electrodes. By means of such a
pumping cell, it is consequently possible to produce the function
of a diffusion barrier, although in contrast to the prior art the
diffusion barrier can still be adjusted or trimmed during operation
of the pumping cell (i.e. in situ).
[0009] The essential advantage of the solid electrolyte gas sensor
according to the invention is the reduction in the number of
contacts. With the proposed sensor, the outlay is also reduced
compared with the calibration step required in the prior art, and
ageing processes of such diffusion barriers are fully avoided or
can be compensated for in situ, so that the sensor according to the
invention is easier to operate compared with the prior art and
actually longer-lasting.
[0010] By means of the gas sensor according to the invention, the
oxygen partial pressure or residual oxygen partial pressure can be
determined quantitatively throughout the entire lambda range. By
modifying the readily accessible outer autonomous pumping
electrode, for example in the form of a mixed potential electrode,
adaptation of the sensor for the detection of further (different)
gas species can also be carried out.
[0011] The present invention furthermore relates to a method for
operating a sensor element according to the invention, or a
corresponding solid electrolyte gas sensor, for the quantitative
detection of oxygen, wherein a constant voltage is applied between
two measurement electrodes and wherein the electrical pumping
current resulting from the applied constant voltage is used as a
measurement variable for the oxygen partial pressure in the exhaust
gas.
[0012] In the method according to the invention, different states
of the autonomous pumping cell can be set by means of the applied
constant voltage.
[0013] In the method according to the invention, a reduced pressure
can furthermore be set in the closed pumping chamber, so that a
positive pumping current is still generated even in relatively rich
exhaust gas, i.e. an exhaust gas with a relatively low air factor
lambda.
[0014] It should be noted that the solid electrolyte gas sensor
according to the invention can be used with said advantages not
only in the field of motor vehicle technology, but also in any
combustion engine machines or burners in which, for example, lambda
probes of the type in question here are employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be explained in more detail below with
reference to the appended drawings with the aid of preferred
exemplary embodiments, by which further features and advantages of
the invention are revealed. In the drawings, corresponding or
functionally equivalent features are provided with the same
reference numbers.
[0016] In detail:
[0017] FIG. 1 shows a longitudinal section through a sensor element
of a wideband lambda probe according to the prior art;
[0018] FIG. 2 shows a longitudinal section through a sensor element
of a proportional probe according to the prior art;
[0019] FIG. 3 shows a cross section through a sensor element of a
mixed potential sensor according to the prior art;
[0020] FIG. 4 shows a longitudinal section through a sensor element
according to a first exemplary embodiment of the solid electrolyte
gas sensor according to the invention;
[0021] FIG. 5 shows a longitudinal section through a sensor element
according to a second exemplary embodiment of the solid electrolyte
gas sensor according to the invention;
[0022] FIG. 6 shows a plan view of a trimmable resistor meander for
calibrating the oxygen transport in a solid electrolyte gas sensor
according to the invention;
[0023] FIG. 7 shows a longitudinal section through a sensor element
according to a third exemplary embodiment of the solid electrolyte
gas sensor according to the invention; and
[0024] FIG. 8 shows typical measurement results when using a solid
electrolyte gas sensor according to the invention for a propane gas
burner.
DETAILED DESCRIPTION
[0025] FIG. 1 schematically shows a sensor element 105 of a
wideband lambda probe according to the prior art in lateral
sectional view. The probe shown therein consists of an
yttrium-doped zirconium dioxide body 110 forming an ionically
conducting solid electrolyte, inside which body is arranged a
cavity (pumping chamber or pumping cell) 115 which is connected via
a diffusion barrier 120 to the exhaust gas to be sensed. The sensor
element furthermore contains an air reference channel 125 connected
to the ambient air. In the exhaust gas, in the cavity 115 and in
the air reference channel 125, a cermet electrode 130, 135 is
respectively arranged, these being connected via separate leads to
electrical connection contacts (pads, not shown here). A heater 140
with associated heater insulation 145 is additionally arranged in
the lower region of the sensor element 105, by means of which the
working temperature of the sensor element 105 can be adjusted.
[0026] In the case of an oxygen-rich exhaust gas, oxygen is
continuously removed electrochemically from the pumping chamber 115
by means of the electrode pair IPE 130 and APE 150, specifically
until the electrode pair IPE 130 and RE 135 is at a voltage of for
example 400 mV. The potential existing on the electrode APE 150 is
then positive, relative to the potential of the electrode IPE 130.
The oxygen diffusion current in this case continues as an
electrically measurable pumping current at the electrodes IPE 130
and APE 150 and is used as a measurement variable for the oxygen
partial pressure in the exhaust gas.
[0027] In the case of an exhaust gas with an oxygen deficit, on the
other hand, the pumping direction is reversed. The potential of APE
150 is then more negative than that of IPE 130. In order to switch
over the APE potential, a regulator is used whose input variable
forms the voltage between RE 135 and IPE 130.
[0028] FIG. 2 shows a longitudinal section through a sensor element
of a proportional probe according to the prior art. Similarly as in
the case of the wideband probe, oxygen is removed from a
diffusion-restricted pumping chamber 200 in the case of
proportional probes. The oxygen diffusion current then continues as
an electrically measurable pumping current between an inner sensor
electrode 205 and an (inner) reference electrode 210 and is used as
a measurement variable for the oxygen partial pressure in the
exhaust gas. Yet since there is no information about the rich or
lean state of the exhaust gas owing to the lack of information
(control variable) from the unloaded Nernst cell, there is in this
case also no possibility of reversing the pumping direction as a
function of the exhaust gas composition into the pumping chamber,
i.e. pumping oxygen electrochemically in or out so as to produce a
wideband probe.
[0029] As will be described in more detail below and as has already
been indicated here, with the inventive arrangement of an
autonomous pumping chamber in such a proportional probe, and the
associated closed pumping chamber, wideband measurement operation
is nevertheless possible with oxygen-deficient and oxygen-rich
exhaust gas, even though this type of sensor has only two contacted
electrodes. By means of the invention, the number of contract lines
can therefore be reduced from three to two (plus the required
heating contacts) with this type of probe.
[0030] FIG. 3 in turn shows a mixed potential sensor known from the
prior art in a view similar to the previous figures. Mixed
potential sensors are constructed from an electrochemical cell,
with a first electrode 300 being arranged in the exhaust gas path.
A second platinum electrode 305 is separated by a solid electrolyte
110 from the exhaust gas space 310 arranged above the first
electrode 300 in this case, and is in communication with the
ambient air by means of an air reference channel (not shown here;
corresponding to the reference "125" in FIG. 2).
[0031] In a mixed potential sensor, there are the following
electrical potential conditions. An electrochemical equilibrium is
set up in the vicinity of the electrode surface of the
catalytically active platinum electrode in the exhaust gas. The
difference between the electrode potentials is given according to
the Nernst equation (Eq. 1).
U N ( p O 2 Exhaust gas ) = k T 4 F ln ( p O 2 Reference p O 2
Exhaust gas ) ( 1 ) ##EQU00001##
[0032] If the outer sensor electrode SE is modified, for example by
applying an additional electrode material or replacing the
electrode material, this electrode no longer behaves in a way
corresponding to an equilibrium electrode; rather, it follows the
properties of a mixed potential electrode whose electrode potential
is determined by the kinetics of the electrode reaction. The sensor
signal U.sub.M is given by the difference between the two electrode
potentials:
U.sub.M(p.sub.o.sub.2.sup.Exhaust
gas)=.phi..sub.SE(p.sub.o.sub.2.sup.Exhaust
gas)-.phi..sub.RE(p.sub.o.sub.2.sup.Reference) (2)
[0033] The reference electrode (RE) is at the reference potential
of the measurement circuit (GND). The reference potential is
consequently set independently of the gas atmosphere.
[0034] Two exemplary embodiments of sensor elements of a solid
electrolyte gas sensor according to the invention will be described
below with reference to FIGS. 4 and 5.
[0035] The sensor element 400 according to the invention is
constructed in a similar way to the types of probes described above
and comprises a pumping chamber 115, a heater 140, an inner pumping
electrode PE2 130 arranged in the pumping chamber, and a further
pumping electrode PE1 405. The pumping electrode PE1 405 is
arranged either in the exhaust gas (FIG. 5) or in the air reference
channel 125 (FIG. 4).
[0036] In order to achieve sufficient ionic conductivity of the
solid electrolyte 110, the sensor element 400 is adjusted to the
required operating temperature by the heater 140.
[0037] In contrast to standard sensors, however, the pumping
chamber 115 is sealed gas-tightly 410 from the exhaust gas. In
addition, there is a further electrode AUPE1 415 and AUPE2 420
respectively in the exhaust gas and in the pumping chamber 115,
although according to the embodiment they are not contacted outward
i.e. from the sensor element to an evaluation circuit, and for this
reason they are referred to below in all cases as "autonomous"
pumping electrodes.
[0038] The gas inflow, or the gas inflow restriction, in this
sensor element 400 is produced by said autonomous pumping cell 415,
110, 420, 115, 410 instead of the diffusion barrier known in the
prior art. A Nernst voltage (two Nernst or oxygen electrodes, for
example Pt-Pt) is formed according to the oxygen concentration
gradient between the exhaust gas and the gas-tight pumping chamber
115, 410, and in the case of a loaded or short-circuited pumping
cell 415, 110, 420 said Nernst voltage causes transport of oxygen
into the pumping chamber 115, 410 or out of the pumping chamber
115, 410 (migration current) without application of an external
electrical voltage.
[0039] As an alternative, a mixed potential electrode (FIG. 3) may
also be used as an outer autonomous pumping electrode (AUPE1), so
that depending on the electrode material the sensor is suitable for
detecting oxygen (mixed potential formation inter alia for HC and
CO with oxygen) and for detecting further gas species (selective
mixed potential formation, for example NH.sub.3, NO.sub.x, CO,
etc.).
[0040] The following may be envisaged as possible electrode
materials for the sensor element according to the invention:
[0041] Nernst electrodes (for example Pt, Pd, Ir, Ta) or
combinations of these materials, or combinations with further
constituents, in particular ones comprising ceramic components such
as so-called "cermets".
[0042] Mixed potential electrodes (for example Au, Ag, Cu, Zn) or
combinations of these and/or the above materials, or combinations
with further constituents, in particular ones comprising ceramic
components such as so-called "cermets".
[0043] The oxygen transport may be adjusted by loading the
autonomous pumping cell 415, 110, 420 by means of a resistor (from
freewheel to short circuit). This may for example be done by using
a trimmable resistor meander (for example laser balancing). In the
event of an unexpected product variance, this may also be used in
the production process as a simple and economical possibility for
sensor calibration (FIG. 6). Under normal production conditions,
however, balancing is usually not necessary.
[0044] The resulting voltage in the case of two oxygen electrodes
is determined by the oxygen partial pressure set up (concentration
and/or change in the absolute pressure). When using a gas-tight
pumping chamber 115, 410 (only defined gas inflow via the
autonomous pumping chamber and by the active pumping process),
electrode voltages of more than |U|>0.9 V may also occur,
compared with the gas inflow restriction by means of a porous
diffusion barrier (according to the prior art) owing to the lack of
convective exchange and consequently reduced or elevated pressure
and/or because of a very small oxygen partial pressure in the
pumping chamber. Thus, a Nernst voltage of more than 900 mV with
respect to an air reference may be achieved even without the
presence of an actual rich gas, resulting from a reduced pressure
in the pumping chamber 115, 410.
[0045] Particular properties and advantages of the autonomous
pumping chamber 115, 410 according to the invention are therefore:
[0046] Oxygen transport is possible without application of an
external voltage or current (otherwise 2 further electrical
contacts would be required for this). [0047] Full separation of the
measurement electrodes from the exhaust gas (no poisoning
phenomena, soot buildup, etc. possible on the measurement
electrodes). [0048] Characteristic curve of the gas inflow (by
oxygen ion conduction) is dependent on the difference in the oxygen
partial pressures (concentration and/or change in the absolute
pressure) between AUPE1 and AUPE2. [0049] When using two Nernst
electrodes, the superposition of an LSF characteristic curve
U.sub.N=f(.lamda.) and a component due to a change in the absolute
pressure is obtained for the autonomous pumping cell. The current
resulting from this in the event of a load or short circuit leads
to oxygen transport through the pumping chamber. [0050] When using
at least one mixed potential electrode, the superposition of a
mixed potential characteristic curve U.sub.N=f(.lamda.) (flattened
LSF characteristic curve) and a component due to a change in the
partial pressure is obtained for the autonomous pumping cell. The
current resulting from this in the event of a load or short circuit
leads to oxygen transport through the pumping chamber. This variant
may be used both as an oxygen sensor and for the detection of
further gas species. [0051] The electrical connection of the two
electrodes belonging to the autonomous pumping chamber (electrode
1, AUPE1|solid electrolyte|electrode 2, AUPE2), besides the variant
described in FIG. 6 which preferably comprises an electrical
resistor in the form of a meander 600 represented therein, may also
be produced directly by using a mixed-conducting solid electrolyte
(ionic and electronic conductivity). In the second said variant
mentioned, the system is therefore short-circuited or loaded by
means of itself. The degree of loading can be set by the level of
electrical conductivity (material properties of the
electrolyte).
[0052] According to an alternative embodiment, the described
autonomous pumping cell 415, 110, 420 may also be used as a
replacement for the diffusion barrier of a standard wideband probe
(LSU) (see also FIG. 7 described below).
[0053] The underlying measurement principle of the described
exemplary embodiments will be presented below with reference to the
example of using the first exemplary embodiment (FIG. 4) for the
quantitative detection of oxygen. For the detection of further gas
species, a similar measurement principle may be employed while
taking account of the modified mixed potential electrodes.
[0054] The gas inflow restriction is set with the aid of the
properties of the autonomous pumping cell 415, 110, 420 (loaded to
short circuit) either directly in the sensor element or, in the
case of contacts fed out of the autonomous pumping cell, in the
evaluation circuit. A constant voltage is applied between the
pumping electrodes PE1 130 and PE2 405, similarly as in the case of
the described proportional probes (so-called LSP operation).
Different states of the closed pumping chamber 115, 410 (various
oxygen concentrations to reduced pressure) may be set according to
the applied pumping voltage.
[0055] According to the gas composition of the exhaust gas and
inside the closed pumping chamber 115, 410, an oxygen ion flow into
the pumping chamber 115, 410 is formed which, owing to the
continuity equation, corresponds to the oxygen ion flow through the
pumping chamber 115, 410. The associated electrical pumping current
of the pumping chamber 115, 410 tapped off by means of PE1 130 and
PE2 405, which is directly proportional to the oxygen ion flow, can
therefore be used as a measurement variable for the oxygen partial
pressure in the exhaust gas.
[0056] In the event of an intentional reduced pressure in the
chamber, a positive pumping current can be generated even with rich
exhaust gas (see the example measurement below). In other cases, a
unique characteristic curve with positive or negative sign is
obtained.
[0057] FIG. 7 represents a sensor element according to the
invention according to a third exemplary embodiment (variant 3) of
the invention, wherein the measurement principles already described
above according to FIGS. 2 and 5 are combined together. Variant 3
is therefore based on the standard LSU regulation principle used in
the wideband probes described above. The associated sensor
characteristic curves are changed according to the properties set
for the autonomous pumping chamber according to the invention (i.e.
electrode material and load), as described above.
[0058] FIG. 8 shows a measurement signal resulting from a step
change in the oxygen excess (lean range) or the oxygen demand (rich
range) with the respective measurement parameters with reference to
the example of a sensor element according to FIG. 4 (variant 1). In
this application example, the closed pumping chamber was arranged
in the exhaust gas stream of a propane gas burner.
[0059] Although the electrode inside the pumping chamber has its
potential less than 1 V below the potential of the air reference
electrode (U.sub.AUPE2-PE2<-1 V), owing to the reduced chamber
pressure intentionally set in this mode and/or because of a very
low oxygen partial pressure, a positive pumping current is
nevertheless achieved which can be assigned to a unique
characteristic curve. In principle, other combinations of a loading
resistor and pumping voltage are also possible. These likewise
result in unique characteristic curves, possibly with positive or
negative signs.
[0060] The sensor variants described here can be used for detecting
the oxygen partial pressure (wideband) inter alia in motor vehicle
tailpipes. In principle, however, depending on the sensor variant
respectively used, and in particular the electrode material used
and the temperature, quantitative determination of various other
gas constituents may also be envisaged, for example: [0061]
combustible gases (hydrocarbons, hydrogen, ammonia, etc.) [0062]
gases containing oxygen (nitrogen oxides, carbon monoxide,
etc.).
* * * * *